What explains the success of Donald Trump? In the first two posts in this series, we discussed two factors. First, most Americans and many Republicans in particular are not orthodox ideologues. Second, white identity and hostility to minority groups are strongly correlated with Trump support.

In this last post, we again draw on decades of research to identify a third important factor: the economic struggles that some Americans are experiencing.

In the same essay in which he identified the general absence of ideological thinking and the prominent role of social groups, political scientist Phillip Converse identified another salient feature of people’s thinking about politics. He called it “the nature of the times.”

He found that people’s opinions of the parties and candidates were often based on how well things were going in the country. Rather than say, “I like the Democrats because they’re liberal,” people said things like “There are more jobs when the Democrats are in power.”

For many voters, the “nature of the times” is best captured by the economy. So there is an extensive literature in the United States and many other countries documenting this basic relationship: Tough times make it tough going for incumbents. In fact, people tend to “vote the bums out” regardless of ideology: Across the world, incumbent parties of all ideological stripes suffered as a result of the Great Recession.

This tendency to vote “retrospectively” — to look at how things have been going recently and reward or punish the incumbent accordingly — is particularly prevalent among voters with less formal education or who pay less attention to politics.

These are exactly the kind of voters who are supporting Trump, who frequently makes statements that describe “the nature of the times.” “Our country doesn’t win anymore” and “Make America great again” are refrains that tell voters that times are bad. It’s a message already in alignment with some features of public opinion—such as the dissatisfied majorities who say that the country is on the wrong track.

Trump has been quick to blame both parties for the widespread belief that the country is on the wrong track. He has suggested he’s in the lead because politicians on both sides of the aisle are “incompetent.” Retrospective voting, by Trump’s account, calls for voting out some Republicans as well.

Nor may it matter that Trump is light on specifics about the policies that will make him “the greatest jobs president God has ever created.” A new book from Christopher Achen and Larry Bartels suggests that citizens do not thoughtfully weigh economic policies in deciding between presidential candidates. Instead, Achen and Bartels show that incumbents are often punished for events well outside of their control—including droughts or even shark attacks.

It’s not surprising, then, that Trump’s support is strongest among those who are struggling. Here are two pieces of evidence.

First, YouGov/Economist polls show that Trump’s gains among Republicans were larger among those who reported that their personal finances had gotten worse, compared to those whose finances had gotten better. The gap is now roughly 20 percentage points.

Of course, this graph can’t help us sort out chicken and egg. Did people who believed their personal finances were worse come to support Trump for that reason, or did people come to support Trump and then, hearing that “we’re not winning,” come to believe that their personal finances weren’t doing so well?

Fortunately, a second piece of evidence can help. The RAND Presidential Election Panel Study draws on participants in RAND’s ongoing American Life Panel, which began in 2006. For about 1,350 people, including nearly 500 who said they were likely to vote in a Republican primary, we know whether they supported Trump in December 2015 and how satisfied or dissatisfied they were about their lives, jobs, income, and economic situation in January 2015.

In other words, we have a measure of life satisfaction that comes months before Trump announced his candidacy and became a dominant part of the GOP race. If Trump does better among people who were dissatisfied at that point in time, we can be more confident that dissatisfaction is driving Trump support.

And that’s exactly what the graph below shows. Trump did about 30 points better among those who, almost one year earlier, were the most dissatisfied with their situation, compared to those who were the most satisfied. Even after taking account of respondents’ level of formal education, a strong relationship remains.

Other evidence tells the same story. Wonkblog’s Jeff Guo noted that, in the Iowa caucus, Donald Trump did better in counties with a lower average income. Political scientist Matt Blackwell showed the same pattern in the South Carolina primary and the Super Tuesday states.

Trump is constantly telling voters how his own personal greatness will lead to prosperity. Not only will he make America great again, but he will make America rich again. It’s a message that appears to resonate among Americans who do not feel prosperous.

Michael Tesler is assistant professor of political science at UC Irvine, co-author of “Obama’s Race” and author of the forthcoming “Post-Racial or Most-Racial? Race and Politics in the Obama Era.”

John Sides is an Associate Professor of Political Science at George Washington University. He specializes in public opinion, voting, and American elections.